The present invention relates to a seat cushion of a passenger seat for use in vehicles and to a method of manufacturing the same.
A seat cushion of a passenger seat for use in vehicles such as passenger cars comprises a cushioned upper body and a lower body beneath the upper body. The upper body provides an occupant comfort when the occupant sits thereon. The lower body gives structural strength and rigidity to the seat cushion. The lower body has brackets for the installation of the seat cushion to a vehicle structural member. The brackets are embedded in the lower body such that portions of the brackets project from the bottom surface of the seat cushion. The top surface and side surfaces of the seat cushion are covered by a trim cover made of covering material such as cloth and leather.
The upper body of the seat cushion is typically formed of soft polyurethane foam while the lower body is formed of rigid hollow plastic, metal member, or high density foam. PCT/CA94/00109 (WO94/19209) discloses that the lower body is formed of rigid polyurethane foam. According to this publication, the formation of the lower body of the rigid polyurethane foam exhibits the following effects:
i) since the lower body is formed of the same material as the upper body, recycling of the seat cushion is simplified as compared to a case that the lower body is formed of a material, such as metal, different from that of the upper body; and
ii) the weight of the seat cushion is lighter than that of the seat cushion of which the lower body is formed of metal. As a result, the reduction in weight of a vehicle is achieved.
However, the recycling of rigid polyurethane foam itself is not easy. In addition, the rigid polyurethane foam has the following disadvantages in producing a molded product as a lower body of a seat cushion.
I. It is impossible to form an inverted-taper-shaped molded product from rigid polyurethane foam. Accordingly, the rigid polyurethane foam gives restraints on the configuration and the construction of the lower body.
II. The lower body is thin and has a large flat surface area. Since the viscosity of foamable liquid of the rigid polyurethane foam is high, the foamable liquid is hard to flow to every corner of a mold. This may be a cause of defective products.
III. It is difficult to control the hardness of the rigid polyurethane foam. Therefore, there is some difficulty in making the lower body having a desired hardness from the rigid polyurethane foam.
It is a first object of the present invention to provide a seat cushion for use in vehicles which can be easily recycled. It is a second object of the present invention to provide a seat cushion for use in vehicles in which the configuration and the construction of a lower body can be relatively easily changed. Other objects of the present invention will be apparent from the following description.
A seat cushion of the present invention includes a lower body and an upper body made of soft polyurethane foam on the lower body. The lower body and the upper body are integrally formed. The lower body is constituted of a polyurethane chip molded product, a polystyrene molded product, a polyethylene molded product, or a polypropylene molded product.
In the method manufacturing the seat cushion of the present invention, after a molded product composing the lower body is placed in a mold, liquid polyurethane material is poured into the mold and is expanded to integrally form the upper body of soft polyurethane foam on the lower body. The molded product composing the lower body is a polyurethane chip molded product, a polystyrene molded product, a polyethylene molded product, or a polypropylene molded product.
The polyurethane chip molded product can be easily recycled. The polyurethane chip molded product is made of soft polyurethane foam which is the same material of the upper body of the seat cushion and is formed by molding the material with a binder. By removing metallic parts such as brackets, the residues are the upper body and the lower body made only of polyurethane as a whole, so eventual recycling of the seat cushion is simplified.
It is easy to form even an inverted-taper-shaped molded product and a large-sized thin molded product from polyurethane chips. The polyurethane chip molded product of which hardness can be easily controlled can provide a lower body of a seat cushion having a desired configuration and hardness.
Carbon dioxide is generated while the liquid polyurethane material is expanded. By ensuring a discharge route of the carbon dioxide, a high quality soft polyurethane foam can be formed. Porous cells of polyurethane chip molded product function as the discharge route of the carbon dioxide, thereby forming the upper body of a high quality soft polyurethane foam.
Though a polystyrene (PS) molded product, a polyethylene (PE) molded product, and a polypropylene (PP) molded product are made of materials different from the soft polyurethane foam of the upper body, the recycling is quite easy because they are thermoplastic resins. Such molded product is recycled after separated from the upper body and removing the brackets of the seat cushion.
The PS molded product, the PE molded product, and the PP molded product can provide even an inverted-taper-shaped molded product and a large-sized thin molded product because of their excellent moldability. Any one of the molded products has low density, thereby reducing the weight of the seat cushion and the vehicle.
The polyurethane chip molded product used in the present invention is preferably made by press-molding chips of soft polyurethane foam together with a binder. It is further preferable that at least some of said chips are chips made by fibrillating soft polyurethane foam.
The soft polyurethane foam composing the upper body preferably has a 25 percent ILD hardness of 60 to 300 N and a density of 20 to 80 kg/m3.
The polyurethane chip molded product constituting the lower body preferably has a 25 percent ILD hardness of 300 N or more, particularly from 1000 to 5000 N and a density of 100 kg/m3 or more, particularly from 150 to 300 kg/m3.